In recent years, interest in the prevention of global warming and the reduction of CO2 emission has been growing. Under such social circumstances, development has been conducted on household fuel cell co-generation systems that are equipment capable of efficiently extracting electric power and heat for household consumption from primary energy such as city gas. Such a system needs to have, for example, certain durable years (in general, 10 durable years are necessary) as commercial equipment to be installed in households.
A fuel cell stack used in such a system as above degrades proportionally to its power generation hours. With the current technology, the life of a fuel cell stack is 40000 to 50000 hours. Assume a case where the system is installed in, for example, a household. In this case, if energy saving is prioritized, it is estimated that power generation hours cumulated in ten years would be approximately 60000 to 80000 hours. As a result, the targeted 10 durable years cannot be achieved.
The above system includes a fuel reformer configured to generate hydrogen from a fuel gas, such as city gas, supplied from an existing infrastructure. Since the fuel reformer has a portion that is heated at high temperature, the possibility of fatigue breakdown is increased when start-up is repeated by a certain number of times.
With the current technology, the system reaches the end of its life after the system performs 4000 to 5000 times of start-ups. In a case where the system is installed in a household, the number of start-ups performed by the system will reach 3650 times in ten years even if the number of start-ups is assumed to be once a day. Considering that there are cases where the system performs start-ups twice or more in one day, then it is possible that the system does not last for ten years. Solving such a trade-off problem is one of the major challenges for putting fuel cell systems into practical use.
In order to solve this problem, for example, Patent Literature 1 discloses a technique in which the power generation hours and the number of start-ups per unit period are restricted and thereby 10 durable years of equipment are realized.
As another example, Patent Literature 2 discloses a fuel cell system and its operation method which take into consideration energy saving and the like.